Conventional chiller units are commonly used to cool the air supply to a building. In a compression type conventional chiller, vaporized refrigerant is compressed in a compressor which causes the refrigerant to heat up. The hot gas is directed to the condenser where the refrigerant is cooled and condenses. Typically the condenser is cooled by water or air. Many such chiller systems utilize cooling towers to provide a supply of cooled water to the condenser to absorb rejected heat. The liquid refrigerant from the condenser passes through an expansion valve into the evaporator. As the fluid passes through the expansion valve, the pressure of the refrigerant is reduced causing vaporization of the liquid, which results in a large reduction in temperature. The cold refrigerant in an evaporator is used to cool a separate circulatory water system (or any other suitable fluid).
The water cooled by the chiller is then pumped to a heat exchanger that is positioned in the flow of the air supply to be cooled. The air passing over the heat exchanger is cooled and is then directed to the various spaces within the building that require cooling. The warmed water exiting the heat exchanger is redirected to the chiller to be cooled again. Conventional chiller units can quickly cool the interior of a structure, but they consume large quantities of electricity, particularly when ambient temperature and humidity are high.
Another type of conventional chiller system commonly used employs an absorptive refrigeration system. This type of system utilizes a heat source to provide the energy needed to drive the cooling system rather than being dependent on electricity to run a compressor as with the chiller system described previously. Absorptive refrigerators are popular in situations where electricity is unreliable, costly, or unavailable, where noise from the compressor is problematic, or where surplus heat is readily available. A widely used gas absorption refrigerator system cools by evaporating liquid ammonia in a hydrogen environment. The gaseous ammonia is then dissolved into water, and then later separated from the water using a source of heat. This drives off the dissolved ammonia gas which is then condensed into a liquid. The liquid ammonia then enters the hydrogen-charged evaporator to repeat the cycle. Other types of systems are also used.
Conventional refrigerant based cooling systems, often referred to as DX (Direct Expansion) systems, are also employed to cool the air supply to buildings. A DX system operates identically to a chiller, with the exception that the evaporator is used to cool an air stream directly (there is no chilled water loop). The condenser of a DX system is also typically air cooled. Like conventional chiller units, DX systems can quickly cool the interior of a structure, but they consume large quantities of electricity, particularly when ambient temperature and humidity are high.
In areas of the world having suitable climatic conditions evaporative coolers are used as an alternative to conventional chillers or DX systems to cool the air supply to residential and commercial buildings. The use of evaporative coolers is a desirable method of cooling air because of their relatively low installation cost, their relatively lower maintenance costs, and their relatively low cost of operation in comparison with conventional chiller units and DX systems. Because evaporative coolers use the latent heat of evaporation to cool process water, such evaporative systems do have some operational limitations and disadvantages. In particular, the cooling effectiveness of an evaporative cooler is dependent on the ambient wet bulb temperature and is greatly reduced as the temperature or humidity, or both, of the ambient air increases. This means that the use of evaporative coolers is limited on days when hot and humid conditions are being experienced, and is impractical in regions experiencing prolonged periods of hot and humid weather. Evaporative cooling units are usually not able to cool a fluid to a temperature less than the wet bulb temperature of the ambient air.
Therefore, there is a need in the art for an evaporative cooling system that can be used alone, or in an assistive manner with a conventional chiller, or with a DX system, that mitigates some of the limitations of existing evaporative systems. It would also be preferable if the new evaporative cooling system had a greater cooling capacity than existing evaporative cooling systems during humid conditions.